Conventionally, an antilock brake system (ABS) of a vehicle is controlled by an ABS control system to avoid wheels of the vehicle to be locked upon sudden braking and assure proper running stability.
Specifically, it is well known as a technique that a wheel speed sensor is provided on each wheel of a vehicle and outputs from the wheel speed sensor are processed by an electronic control system to control the ABS. The minimum, maximum or average output value of the wheel speed sensor is selected as a vehicle speed to calculate slipping rate based on the vehicle speed and a wheel speed of each wheel to judge whether any wheel skids or not to start ABS control (for example, see Patent Document 1).
Traditionally, a retarder is provided on vehicles such as a dump truck to avoid overrun of an engine when the vehicles run down a long slope carrying a heavy load. The retarder is controlled by a retarder controller. The retarder controller detects rotation frequency of an output shaft of an engine and an input shaft of a transmission by a sensor and the like. When the detected rotation frequency of the shaft exceeds a certain threshold, the retarder is started to be operated to avoid overrun of the engine (for example, see Patent Document 2).
Cooperation between an ABS and a retarder simultaneously realizes constant speed running of a vehicle and proper braking force for the vehicle which avoids wheels to be locked.    [Patent Document 1] JP-UM-A-7-14180 ([0019]-[0020])    [Patent Document 2] JP-A-10-198417 (FIG. 2, page 2)